Al-Co Alloys Prepared by Vacuum Arc Melting: Correlating Microstructure Evolution and Aqueous Corrosion Behavior with Co Content

Corrosion Behavior of As-Cast and Heat-Treated Al-Co Alloys in 3.5 wt% NaCl

The present work evaluates the effect of Co content on the microstructure and corrosion performance of Al-Co alloys of various compositions (2-32 wt% Co), fabricated by flux-assisted stir casting. A preliminary investigation on the effect of heat treatment (600 °C, up to 72 h) on the microstructure and corrosion behavior of Al-20 wt% Co and Al-32 wt% Co was also conducted. The Al- (2-10) wt% Co alloys were composed of acicular Al9Co2 particles uniformly dispersed in an Al matrix. The Al-20 wt% Co and Al-32 wt% Co alloys additionally contained Al13Co4 blades enveloped in Al9Co2 wedges. Heat treatment of Al-20 wt% Co and Al-32 wt% Co led to a significant reduction in the volume fraction of Al13Co4 and a decrease in hardness. Al-Co alloys with high Co content (10-32 wt% Co) exhibited greater resistance to localized corrosion in 3.5 wt% NaCl, but lower resistance to general corrosion compared to the (0-5 wt% Co) alloys. Heat treatment led to a slight increase in the corrosion resistance of the Al-Co alloys. The microstructure of the produced alloys was analyzed and correlated with the corrosion performance. Finally, corrosion mechanisms were formulated.

Aluminium Matrix Composites Reinforced with AlCrFeMnNi HEA Particulates: Microstructure, Mechanical and Corrosion Properties

Novel aluminium matrix composites have been fabricated using a powder metallurgy route with reinforcement phase particles of high entropy alloy (HEA) consisting of third transition metals. These new composites are studied as far as their microstructure (SEM, XRD), basic mechanical properties (hardness, elastic modulus) and creep response using nanoindentation techniques are concerned. Wear (sliding wear tests) and corrosion behaviour (in 3.5 wt.% NaCl environment) were also assessed. It was observed that, microstructurally, no secondary intermetallic phases were formed. Hardness and wear resistance seemed to increase with the increase in HEA particles, and in terms of corrosion, the composites exhibited susceptibility to localised forms. Nanoindentation techniques and creep response showed findings that are connected with the deformation nature of both the Al matrix and the HEA reinforcing phase.

A Critical Review on Al-Co Alloys: Fabrication Routes, Microstructural Evolution and Properties

Al-Co alloys is an emerging category of metallic materials with promising properties and potential application in various demanding environments. Over the years, different manufacturing techniques have been employed to fabricate Al-Co alloys, spanning from conventional casting to rapid solidification techniques, such as melt spinning, thus leading to a variety of different microstructural features. The effect of the fabrication method on the microstructure is crucial, affecting the morphology and volume of the precipitates, the formation of supersaturated solid solutions and the development of amorphous phases. In addition, the alloy composition has an effect on the type and volume fraction of intermetallic phases formed. As a result, alloy properties are largely affected by the microstructural outcomes. This review focuses on highlighting the effect of the fabrication techniques and composition on the microstructure and properties of Al-Co alloys. Another goal is to highlight areas in the field that are not well understood. The advantages and limitations of this less common category of Al alloys are being discussed with the scope of future prospects and potential applications.

Aqueous Corrosion of Aluminum-Transition Metal Alloys Composed of Structurally Complex Phases: A Review

Complex metallic alloys (CMAs) are materials composed of structurally complex intermetallic phases (SCIPs). The SCIPs consist of large unit cells containing hundreds or even thousands of atoms. Well-defined atomic clusters are found in their structure, typically of icosahedral point group symmetry. In SCIPs, a long-range order is observed. Aluminum-based CMAs contain approximately 70 at.% Al. In this paper, the corrosion behavior of bulk Al-based CMAs is reviewed. The Al-TM alloys (TM = transition metal) have been sorted according to their chemical composition. The alloys tend to passivate because of high Al concentration. The Al-Cr alloys, for example, can form protective passive layers of considerable thickness in different electrolytes. In halide-containing solutions, however, the alloys are prone to pitting corrosion. The electrochemical activity of aluminum-transition metal SCIPs is primarily determined by electrode potential of the alloying element(s). Galvanic microcells form between different SCIPs which may further accelerate the localized corrosion attack. The electrochemical nobility of individual SCIPs increases with increasing concentration of noble elements. The SCIPs with electrochemically active elements tend to dissolve in contact with nobler particles. The SCIPs with noble metals are prone to selective de-alloying (de-aluminification) and their electrochemical activity may change over time as a result of de-alloying. The metal composition of the SCIPs has a primary influence on their corrosion properties. The structural complexity is secondary and becomes important when phases with similar chemical composition, but different crystal structure, come into close physical contact.

Microstructure and Corrosion Performance of Aluminium Matrix Composites Reinforced with Refractory High-Entropy Alloy Particulates

Novel aluminium matrix composites reinforced by MoTaNbVW refractory high-entropy alloy (HEA) particulates have been fabricated by powder metallurgy. The microstructure of the produced composites has been studied and the corrosion behaviour assessed in 3.5% NaCl solution. The composites exhibited low porosity, good homogeneity, few defects, and good distribution of the reinforcing phase in the Al matrix. No secondary intermetallic phases have been formed while the interface between matrix/reinforcement showed good bonding with no signs of reactivity. Increasing the volume of the reinforcing phase leads to increased hardness values. Al-HEA composites exhibited susceptibility to localised forms of corrosion in 3.5% NaCl solution. The microstructure has been analysed and corrosion mechanisms have been formulated.

Relationship between Phase Occurrence, Chemical Composition, and Corrosion Behavior of as-Solidified Al-Pd-Co Alloys

The microstructure, phase constitution, and corrosion performance of as-solidified Al₇₀Pd₂₅Co₅ and Al₇₄Pd₁₂Co₁₄ alloys (element concentrations in at.%) have been investigated in the present work. The alloys were prepared by arc-melting of Al, Pd, and Co lumps in argon. The Al₇₄Pd₁₂Co₁₄ alloy was composed of structurally complex ε_n phase, while the Al₇₀Pd₂₅Co₅ alloy was composed of ε_n and δ phases. The corrosion performance was studied by open circuit potential measurements and potentiodynamic polarization in aqueous NaCl solution (3.5 wt.%). Marked open circuit potential oscillations of the Al₇₀Pd₂₅Co₅ alloy have been observed, indicating individual breakdown and re-passivation events on the sample surface. A preferential corrosion attack of ε_n was found, while the binary δ phase (Al₃Pd₂) remained free of corrosion. A de-alloying of Al from ε_n and formation of intermittent interpenetrating channel networks occurred in both alloys. The corrosion behavior of ε_n is discussed in terms of its chemical composition and crystal structure. The corrosion activity of ε_n could be further exploited in preparation of porous Pd–Co networks with possible catalytic activity.